Livestock manure is an excellent biological fertilizer that has been used since the beginning of agriculture. Livestock manure has high value in maintaining and fertilizing a soil because of the plant nutrients, humus, and organic and fibrous substances contained in it. It is known that a high percentage of the nitrogen, phosphorus, and potassium fed to dairy cattle for example, are excreted in manure. These elements are basic nutrients that plants need for healthy growth.
The fertilizing properties of cattle, poultry and swine manure, however, are depending upon several factors. It has been found for example, that the fertilizing properties of manure depend on the conditions in which the manure is stored prior to spreading it on crop fields.
When the manure is exposed to air, a chemical process takes place and causes nitrogen to be released into the atmosphere under different forms. Before the manure can be spread on a field, the proper balance in the fertilizing elements must be restored by adding chemical nitrogen into the manure. This additional operation is costly. Therefore there is a first incentive for farmers to carefully store the manure in a reservoir that is airtight to some extent, to minimize loss of nutrients.
In another aspect, the accumulation of rainwater and melting snow inside an uncovered manure reservoir reduces the capacity of the reservoir and increases the handling and transport costs for spreading this diluted manure on a field. Therefore this is a second incentive for farmers to store the manure under an impermeable cover to prevent dilution with water.
It is believed that the preferred manure storage installation to prevent degradation of the fertilizing elements found in livestock manure and to prevent dilution of manure with rain water and melting snow, includes a concrete reservoir covered by a flexible impermeable membrane floating over the content of the reservoir. This type of cover reduces the air space at the surface of the reservoir, and has the ability to rise with the accumulation of material inside the reservoir. The preferred membrane cover is strong enough to support several workers walking on it. Any accumulation of water at the surface of such membrane can be pumped out using a portable sump pump, and any snow can be removed by shoveling or blowing it if required.
Another requirement to preserve the fertilizing properties of cattle manure during storage consists of periodically agitating the content of the manure reservoir with a portable pumping and mixing device to promote fermentation. In common practice, this agitation is rarely effected because of the odor that is generated from the reservoir.
Preferably, a manure reservoir has a hatchway within the perimeter thereof to insert a portable pumping and mixing device therein. This hatchway is preferably isolated from the bio-gas floating at the surface of the reservoir such that this bio-gas and associated odors do not escape into the environment or do not mix with outside air every time the hatch doors are opened.
Although the prior art contains numerous suggestions on floating membrane covers for installation over industrial, municipal and agricultural liquid reservoirs, these prior art installations do not provide for a hatchway therein for introducing a portable pumping and mixing device inside the reservoir. In that respect, the following documents represent a good inventory of a first type of membrane covers available in the prior art.    U.S. Pat. No. 3,103,083 issued to F. Seeger on Sep. 10, 1963;    U.S. Pat. No. 3,815,367 issued to J. B. Collins et al. on Jun. 11, 1974;    U.S. Pat. No. 3,980,199 issued to W. B. Kays on Sep. 14, 1976;    U.S. Pat. No. 3,991,900 issued to N. R. Burke et al. on Nov. 16, 1976;    U.S. Pat. No. 4,139,117 issued to H. S. Dial on Feb. 13, 1979;    U.S. Patent RE 30,146 reissued to H. S. Dial et al. on Nov. 13, 1979;    U.S. Pat. No. 4,230,580 issued to C. Dodson on Oct. 28, 1980;    U.S. Pat. No. 4,438,863 issued to J. V. Wilson et al. on Mar. 27, 1984;    U.S. Pat. No. 4,446,983 issued to D. H. Gerber on May 8, 1984;    U.S. Pat. No. 4,476,992 issued to D. H. Gerber on Oct. 16, 1984;    U.S. Pat. No. 4,503,988 issued to D. H. Gerber on Mar. 12, 1985;    U.S. Pat. No. 4,603,790 issued to D. H. Gerber on Aug. 5, 1986;    U.S. Pat. No. 4,672,691 issued to C. J. DeGarie et al. on Jun. 16, 1987;    U.S. Pat. No. 5,080,786 issued to D. De Lima on Jan. 14, 1992;    U.S. Pat. No. 5,212,090 issued to R. Landine et al. on May 18, 1993;    U.S. Pat. No. 5,505,848 issued to R. Landine et al. on Apr. 9, 1996;    U.S. Pat. No. 5,562,759 issued to W. D. Morgan et al. on Oct. 18, 1996;    U.S. Pat. No. 5,587,080 issued to R. Landine et al. on Dec. 24, 1996;    U.S. Pat. No. 6,338,169 issued to C. J. DeGarie on Jan. 15, 2002;    U.S. Pat. No. 6,357,964 issued to C. J. DeGarie on Mar. 19, 2002;    U.S. Pat. No. 6,451,206 issued to R. Charbonneau on Sep. 17, 2002;    U.S. Pat. No. 6,497,533 issued to C. J. DeGarie et al. on Dec. 24, 2002;    U.S. Pat. No. 6,524,029 issued to J. E. Nobert et al. on Feb. 25, 2003;    U.S. Pat. No. 6,558,548 issued to F. Svirklys et al. on May 6, 2003.
Other prior art documents disclose openable portions in a second type of membrane covers mounted over industrial, municipal or agricultural reservoirs. These documents are as follows:    U.S. Pat. No. 6,324,792 issued to C. J. DeGarie on Dec. 4, 2001;    U.S. Pat. No. 6,389,757 issued to C. J. DeGarie on May 21, 2002;    U.S. Pat. No. 6,612,079 issued to C. J. DeGarie on Sep. 2, 2003.
A third type of reservoir for storing livestock manure has an access well extending vertically alongside the reservoir. The well contains pipes and a nozzle by which a circulation can be created inside the reservoir to agitate the content of the reservoir. This installation is described in GB Patent Application 2,072,649, published by L. Mellen on Oct. 7, 1981.
A flexible floating membrane does not lend itself to the installation of a hatchway there through. A flexible floating membrane is subject to dynamic stresses from wind, snow and ice loads, and static stresses from its own weight. Therefore it is important that the perimeter of the membrane material be uniformly fastened along the wall of the reservoir.
It is believed that a hatchway structure within the perimeter of a reservoir has never been developed in the past because of the problems associated with the protruding features of a hatchway structure, and the stress concentration points in the membrane cover caused by such protrusions.
The existing flexible floating membrane covers of the first type mentioned above have at least one structural feature in common. The edges of the flexible membrane are uniformly supported along the walls of the reservoirs on which they are mounted. The perimeters of these reservoirs do not have any protruding feature thereon. The perimeter of such reservoir is smooth and has even anchor-bolt-spacing to retain the membrane cover uniformly.
The covers of the prior art reservoirs having openable portions comprise a roof structure supporting the membrane cover above the liquid level of the reservoir. In these installations, a substantial amount of bio-gas can accumulate between the surface of the material in the reservoir and the membrane cover. When the cover is opened, this bio-gas can escape outside the reservoir. Therefore this type of openable cover is not appropriate for minimizing the loss of nutrients from livestock manure stored inside the reservoir.
In the third type of prior art reservoir mentioned above, the vertical access well is located outside the manure reservoir. It is believed that this access well can only provide for an indirect access to the reservoir, and a conventional pumping and mixing device introduced therein can only achieve limited performance.
For all these reasons, it is believe that a need exists for a floating membrane cover that can be installed on existing open-top manure reservoirs and in which a hatchway and an airtight compartment can be mounted without exposing the flexible membrane to damaging concentrated stress.